[D&D 3.5] Idea for an alternative polymorph rules game-breaking?

[Dziadek]

In D&D 3.5, I know that polymorph spells have dozens of rules, to ensure that they aren't too powerful or game-breaking when used by Player Characters, but I was wondering why just 3 rules for those spells wouldn't suffice:

1. Player Character can only polymorph into a creature, whose Challenge Rating (after subtracting class levels) is smaller or equal to his own CR

2. Player Character can only polymorph into creature, whose kind he has encountered before (even if it was just few moments ago)- so he knows something about its appearance; no need of perfect knowledge of its anatomy- the spell does the rest- unless, for example, a person who has seen said creature, draws it/ builds a model of it/ creates an illusion of it, to show you- and that representation is TOO different from the actual creature- in that situation, craft (or caster level) checks would be used to determine the similarity of the representation to the creature. Verbal description of the creature isn’t enough (since everyone imagines same things differently)

3. After polymorphing, Player Character retains all of the creature’s abilities (at the same time losing all his previous abilities and stats- but he can willingly change back into his original form), that are solely determined by its race- meaning: if said creature possesses class levels (not counting the first one; some creatures cannot NOT HAVE class levels), Player Character retains only those abilities, skills, feats, Hit Points and ability scores, which would be possessed by it, if you subtracted all (but one) of its class levels and special effects it had undergone since birth (like, got its ability scores increased permanently, by the means of the spell ‘Wish’)

Quoting Rich, about one of the ways the original Polymorph spell could be broken:

“…currently polymorph any object can turn a human into a Firbolg permanently (since a giant might be considered "related" to a human, which makes a total Duration Factor of 9). What's more, PAO will actually give your fighter friend a BOOST to his Intelligence, for free, when you permanently polymorph him into a Firbolg. Who thought THAT was a good idea??”

If the rules I listed above were being used, then, by my thinking, if a character turns into a creature, whose CR is equal to his own, and- while the creature itself wasn’t breaking the game- the character did break it, then the CR that was assigned to said creature isn’t trustworthy, and should be revised- then even a permanent polymorph wouldn’t break the game.

(When you think about it, the proper working Polymorph spell should work like the ‘Elemental Rock-Paper-Scissors’ because it would not increase the overall power of a character, but just move it to different areas)

I’d like to make myself clear: I am not pointing out, that everyone designing the game has been pointlessly working hundreds of hours on the rules, when only a few minutes of work was enough- I just once thought about simplifying the annoyingly-complicated polymorph spell rules and wanted to create the ones that- at least at the first glance- looked balanced.

I would like to know the most eye-stabbingly-painful examples how the rules written above could be broken- I am very curious, and not patient enough to dig through every page of core rulebooks alone.

[Ingus]

Wait: CR is not an index of how good a monster is as PC (that is LA), but how good a monster is as challenge. Take vampire (providing excluding the "enters only if invited" thing): as a challenge, it is better than a human, but as a PC he avoid death by combat, he has wonderful ability boosts and he can build up his private army by creating more vampires.
Way better, take Greater Doppleganger. He is CR 12 and, as top ability, he has the power to subsume perfect identity, feats and class abilities of a humanoid or monstruous umanoid of whom he ate the brain.
Think about it: with the aid of your party, you can easily bring down a 14th level wizard. Then you eat his brain. Then you cast as a 14th level wizard. Then you kill a 14th level psion. So you cast as a 14th level wizard or a 14th level psion. Then again you kill a 15th level warblade (you've becoming better). Now you can boost yourself as a 14th level wizard, then as a 14th level psion and then again going melee as a 15th level warblade. Repeat ad libitum and you'll break the game mercylessy, way worst than a 12th level wizard, to say.

So, CR doesn't help here. Basicly, the rule of previous knowledge (I use knowledge checks to be beaten by 10 or more) is very sensible and, outside heavy optimization, it allows a decent balance.

[Dziadek]

Wait: CR is not an index of how good a monster is as PC (that is LA)

If the CR was changed into LA in my rules, what other problems would they still have? (if we were comparing PC's level+LA and Monster's LA)

edit: okay, found first complication: undead and were-creatures are only listed as templates- so deleting the class levels is out of the question.

[Gnaeus]

The houserule my game uses is that Polymorph type spells give a maximum bonus of (Spell level x2) which can be applied to Str, Con, Dex or NA. This prevents a 6 strength wizard from turning into a 28 strength giant, means that the spell is best used as a buff for melee types instead of a self-buff, and keeps the power level down. Heighten spell is therefore usable to increase that bonus.

The similar Pathfinder nerf gives static bonuses based on type and size, instead of determining them based on the individual creature. So turning into a large giant might be +4 Str, +2 Con, +2 NA (just making that up, didn't check the PFSRD), but that would be the same bonus if you turned into a hill giant or an ogre. It is a little weaker than our game's rule, but is a lot less bookkeeping, since a PC can calculate out his giant form stats once, and doesn't have to keep changing them based on whether he is a hill giant or a fire giant.

[bokodasu]

Funny, my DM was trying out a system almost exactly like this - I broke it for him 20 different ways in five minutes. Not all monsters have LA, because many of them aren't meant to be played. And both the LA and the CR system are kind of whacked; an hour with the Monster Manual and your players will have a form that solves any problem you throw at them.

[grimbold]

polymorph is broken in CONCEPT as well as in other ways, the best thing to do is ask your players to play nice and cross your fingers